1. Field of the Invention
The present invention relates to a process and an apparatus for producing a functional material having various types of excellent photocatalytic activity, such as antimicrobial (bactericidal) activity, deodorant activity, and antifouling activity, useful for waste water treatment, purification of harmful gases and the like.
2. Background Art
In recent years, environmental pollution, for example, water pollution created by domestic waste water, industrial waste water or the like, offensive odor, or contamination with bacteria, typified by MRSA, or mold in living spaces and working spaces has been increased and has become a social problem.
Photocatalysts have drawn attention as materials that, upon light irradiation, cause adsorption of oxygen molecules on bacteria, mold, and organic compounds, such as offensive odor components, or desorption of oxygen molecules therefrom and accelerate the decomposition (oxidation) of the organic compounds. A number of attempts have been made to fix a photocatalyst on the surface of a substrate to clean the surface of the substrate.
PCT/WO 96/29375 discloses that the surface of a photocatalyst-containing layer provided on the surface of a substrate exhibits high hydrophilicity (for example, a contact angle thereof with water of not more than 10 degrees) in response to photoexcitation of the photocatalyst. This property can be utilized to improve antifogging properties and ensuring of visibility of transparent members, such as glasses, lenses, and mirrors, to improve water cleanability and rainfall cleanability of the surface of articles and to improve other properties.
Functional materials utilizing the function of the photocatalyst have hitherto been produced by providing a coating liquid containing a photocatalytic metal oxide or a precursor of the photocatalytic metal oxide, coating the coating liquid, and drying or sintering the coating. For example, a titania sol prepared from a titanium alkoxide and an alcoholamine or a sol prepared by dispersing particles of TiO2, ZnO, SrTiO3 or the like in an aqueous solvent has been coated onto the surface of a substrate followed by drying or sintering. More specifically, as disclosed in Japanese Patent No. 2517874, the production process of functional materials comprises: coating a titania sol onto a substrate; heating the coated substrate in such a manner that the temperature is gradually raised from room temperature to a final temperature of 600 to 700xc2x0 C. to perform firing, thereby fixing the photocatalyst onto the substrate.
The present inventors have now found that functional materials having satisfactory photocatalytic activity can be efficiently produced by rapid heating. They have further found that rapid heating immediately after, that is, successively from, the production of the substrate can realize the production of functional materials having photocatalytic activity in more efficient manner. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide a process and an apparatus for producing a functional material having a satisfactory level of photocatalytic activity.
According to one aspect of the present invention, there is provided a process for producing a functional material having photocatalytic activity, comprising the steps of: coating a photocatalyst coating composition comprising a photocatalytic metal oxide and/or a precursor of the photocatalytic metal oxide onto the surface of a substrate; and
rapidly heating the surface of the coated substrate to fix the photocatalaytic metal oxide onto the surface of the substrate.
According to another aspect of the present invention, there is provided an apparatus for producing a functional material having photocatalytic activity, said apparatus comprising at least
coating means for coating a photocatalyst coating composition comprising a photocatalytic metal oxide and/or a precursor of the photocatalytic metal oxide onto the surface of a substrate and
heating means for rapidly heating the surface of the coated substrate to fix the photocatalytic metal oxide onto the surface of the substrate.
According to the process and apparatus of the present invention, a photocatalytic metal oxide can be surely fixed in a short time on the surface of a substrate, and, in addition, a functional material can be obtained which has high surface smoothness, possesses high photocatalytic activity, and high abrasion resistance and chemical resistance. Furthermore, the process and apparatus of the present invention can reduce the size of the production apparatus used and can realize simplification of the production process and space saving. Furthermore, shortening of the time taken for heating can advantageously contribute to a reduction in cost and a reduction in the amount of the exhaust gas emitted.